Synthesis of pyrido[2,1-a]isoquinolin-4-ones and oxazino[2,3-a]isoquinolin-4-ones: New inhibitors of mitochondrial respiratory chain

•Pemberton method has been applied to obtain benzo[a]quinolizines.•Synthesized compounds were assayed for their ability to inhibit mitochondrial respiratory chain.•The oxazinone derivatives displayed activity in the low micromolar range.•Oxazinone derivatives revealed a potency in the same tendency of the less toxic antitumor agents.•The furan ring in C2 position of the oxazino-isoquinolin-4-ones provided the most potent compound.

Benzo[a]quinolizine is an important heterocyclic framework that can be found in numerous bioactive compounds. The general scheme for the synthesis of these compounds was based on the preparation of the appropriate dihydroisoquinolines by Bischler–Napieralski cyclization with good yields, followed by the Pemberton method to form the oxazinones or pyridones derivatives via acyl-ketene imine cyclocondensation. All the synthesized compounds were assayed in vitro for their ability to inhibit mitochondrial respiratory chain. Most of the tested compounds were able to inhibit the integrated electron transfer chain, measured as NADH oxidation, which includes complexes I, III and IV, in the low micromolar range. Oxazino[2,3-a]isoquinolin-4-ones displayed greater activity than their pyrido[2,1-a]isoquinolin-4-ones analogs. Indeed, the presence of a furan ring in C2 position of oxazino[2,3-a]isoquinolin-4-ones provided the compound (1g) with the most potent biological activity. Therefore, these compounds and especially the oxazinone derivatives are in the tendency of the new less toxic antitumor agents that target mitochondrial electron transport chain in a middle range potency.

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